Insulating enamel for electric conductors



1 y 1943- H. J. KAUTH 2,323,333

INSULATING ENAMEL FOR ELECTRIC CONDUGTORS Filed June 22, 1939 CONDUCTOR /N$ULA7'/ON COAT/NC COMPRISING A DRV/NG-O/L MOD/F/ED AL/(VD RES/N COMB/NED WITH A CONDENSATE OF FURFURYL ALCOHOL CONDUCTOR INSULAT/ON INVENTQR HENRY J. KAU-TH TTORNEY Figure 1. 1 a

I illustrative" purp limitation; I

Patented July 6, 19 43 INSULATING ENAMEL FOR ELECTRIC:

CONDUCTORS Henry J. Kauth, Rome, N. Y., assignor to General Cable Corporation, New York, N. Y., a' cor ora- "-tlon oi! New Jersey Application June 22, 1939, No. 280,5'i5 I scams. (or. 174-125) This invention relates to insulating enamels (or coating electrical conductors and other articles; to the method of makin and applying the enamel; and to the article produced; and has for an object the provision of improvements in this art. In particular, the invention provides an insulating enamel which has good electrical properties, including high dielectric strength; which has good adhesion; which has high heat resistance; which is very tough and hard; which has good flexibility; which is unusually resistant to solvents; which is low 'in cost, and which can be applied at a much higher speed than enamels now available, or can bebaked at much lower temperatures. I

An illustrative embodiment of the invention selected merely for descriptive purposes is sh wn in the accompanyng drawing, in which:

"Figure 1 is' a side elevation of an enamel insulated conductor, the insulation-coating 'being out back so as to disclose the conductor; and

Figure 2 is across section on the "line 2-4 of r The legends appearing on the drawing are for es only and are not byway of In'-- the 1 conventional or commonly practiced method-"of en'ameling wires; :afllm of varnish is applied-to the wire and thensubje'cted to a temperature'-of-from"300 C.to500'-'C.in order-to bake the varnish film;- the temperature and time being"regulated=to securethe desired properties. The most widely-usedmaterials for" forming enamels. are the'oleo-resino'usvarnishes consist- 'ing" of drying oilssuchas-China WoQd; perilla, linseed. 'soy bean, etc.,' combined withs uch gums as kauri, manila, congo copal, etc.,'and thinned with suitable solvents. Durin recent years,cer-. tain synthetic resins have in somev casesreplaced all or part of the natural gums usedf The oilsoluble,=modified phenol-aldehyde resins and the drying-oikmodified' alkyd resins are examples of such synthet c substitutes. materials require the high temperature treatment of the natural materials, since these modified enamels are essentially oleo-resinous varnishes.

The conventionalenamels described have certain definite limitations whch have not been re" moved or greatly expanded by the efiorts of manufacturers to improve these products. From the standpoint of plant operation, the relatively long time and high temperature required to bake these enamels to a suitably hard condition, are limita-'- tions which greatly aflect the economical pro- However, all of these.

duction of enameled wires.- The maintenance of enamel ovens at the high temperatures required results in high heat loss and this-loss cannot be compensated by greatly increased production speeds because the conventional materials, even in their highest state of development, require a relatively long time for their conversion to the solid non-tacky condition; Also,- the conventional materials have limitations" which prevent the attainment of the ultimate properties sought in the enamel film.

As is well known by users of enameled wire, it is particularly desirable that the insulating film be very hard, tough and abrasion resistant and more especially that these properties are retained when the enameled wire is subjected to the action of solvents such as those found in the varnishes, lacquers and [other coil treating ',com-

poundsused. during manufactureas well as any solvents which maybe encounteredlater durin the. normaloperation' or useo f the wirel Con- ,yenao ai enemas aradeiinitelwweak wa rehe s l s .th.-{ a n l dushn ss gland abrasion resistance of these. materials are much .ijelow "the desired standards and especially be- @1 hese P o r i s are, tim com te l en' he, ms tesgbl te with? cti 'Q' ,1 I, A few'ge mpi W 11,illness-gent,

orities of the: products of thisiinvention over conventional materials.

1. DRYING ilnnfB-sxm'c Srnrm I dfi edl'ta rri'onai jlt faster drying conventional enamels a1 fihn 0,0005? thick to aQtalck-Qiree, conditionwas f ound I to be 60'minutes.

commercial enamel o'ven,'jat' 310'? C; satisfactory At 100 0. the timerrequ'ired 01 dryth'e enamel 4o 'of'this invention" in 'afilm 0.0005" thickto a tack-free condition'was round lt'ofbe Zminutes,

In ashort tube, similar. to, but. smaller' than a conversion of a fast-baking,.conventional enamel could be made at amaximuin speed of" 1 it. per

minute. Under identical baking conditions in the same tube the enamel of this invention was An idea of the comparative.=merits of. consatisfactorily converted at a speed, of 35ft. per minute. s.

' ,7 2. sotvsnr Resrsrsncn ventional enamels and theenamel of'this invention with respect to solvent resistance can-be obtained from the following tests in which three different well-baked and aged samples of convarious ventional enameled wires were immersed in 'solvents, together with samples of wire finished with the new enamel and the film properties after immersion determined by scraping the films with a standard scrape test-fixture having a 10 oz. load on the knife edge. In the table. indicates that the film was removed completely to the copper and N indicates that the film was not in any way affected by the scrape test.

The time of immersion is shown.

i Conven- Conven- Conven New tional A tional B tional O enamel Minutes (0) Minutes (0) Minutes (0) Hours (N) cetone ii 6 3 72 Ethyl acetate- 6 5 .5 J Benzol 5 5 6 Toluol 7 b 6 chloroform... 3 3 2 rivatives, including furan C4.Ha.O.H., furfural C4.II:.O.CI-IO, and furfuryl alcohol C4.H:.O.CH.2OH,

which contain the furan nucleus or furan residue 04.1130, that is, diagrammatically,

nc--cn o have properties which suggest the possibility of their use as a low temperature baking enamel.

As shown in the structural formula above, the

furan derivatives contain a conjugated diene system in a hetero cyclic group. This particular structure makes it active in regard to both polymerization and oxidation. Its easy polymerisation and the rapidity of a further conversion to insoluble, infusible forms when the partially condensed material is heated in air at low temperatures, constitute the basis of the present attack on the problem of providing a quick setting, low temperature baking enamel- The fact that heating of the furan derivatives induces condensation and finally resinification suggests that if furfuryl alcohol, for example, were simply aplied as a coating on an object and then heated, there should be formed on the ob- .iect a film of the resinified furfuryl alcohol.

However, if an attempt is made to coat a wire I and bake at once at even a reasonably low temperature, say 170-180" C. for furfuryl alcohol, the coating material will all be evaporated. This is true because furfuryl alcohol boils at 170.2 C. and has a relatively high vapor pressure even below itsboiling point, and resinification or polymerization by heating requires a much longer time than is required for the complete volatilization of any film of ordinary furfuryl'alcohol on a wire where a large surface is exposed for evaporation.

In order to overcome this difiiculty the present invention, first of all, provides for the partial condensation, polymerization or resiniiication of the substance before it is applied to the wire or other object on which it is to be baked. The partial condensation converts the substance from a thin, mobile liquid of low boiling point and high vapor pressure to a very viscous oil or semisolid material of high boiling point and very low vapor pressure. This material can now be ap-.

has been shown to be one of the important features of the invention. This preliminary partial condensation can be carried out in several ways as will be shown presently.- The preliminary condensates formed by any of the following processes can be combined with modifying materials as will be shownlater:

l. CONDENSATION BY Usr: or HEAT ALONE It has been found that furfuryl alcohol can be condensed to form the desirable initial condensates of this invention by heat alone without the addition of any foreign materials as ca alysts. Because this method does not introduce any catalyst which could cause instability in the finished enamel or in the enameled wires, it is not necessary to give the products of this process any special treatment in order to guard against such deteriorating influences. An example of the practice of this process follows:

Example #1 Furfuryl alcohol is charged into a pressure kettle and heated until the temperature reaches lilo-210 C. The pressure gradually builds up even when the temperature is held constant, due to the production of water as a by-product of the reaction. The vapor in the kettle is allowed to leak slowly into a condenser during the heat- ,ing and the pressure can be maintained at any desired level by adjusting the rate of leaking of the vapor. The distillate issuing from the com denser'consists essentially of a mixture of water and furfuryl alcohol. The latter can be recoveredfrom themixtureanduseda'a'ain. Theviscosity of the liquid in the kettle increases progressiv'ely as the condensation reaction proceeds. After about twelve hours of heating. the evolution of water diminishes sharply. The condensation productat this stage is a very'viscous oily -material or a soft semi-solid which dries rapidly when spread in a thin film and exposed to air. The time and temperature of the reaction can the same in all cases. The product can be dissolved in acetone, ethyl acetate, benzoi, toluoi and other common solvents.

v 2. CONDENSATION av Us: or. Vote-run CArAaYsrs Example #2 Parts by weight Furfuryl alcohol 98 Formic acid 46 Ethyl acetate (solvent) 150 The mixture is heated under a reflux condenser for about one hour at 110 C. The heating is then discontinued and the liquid filtered to produce a clean solution of the initial condensates. when the solvent is evaporated from this solution a soft, solid, brownish colored residue or film is left. This film rapidly converts to the insoluble and infusible condition when heated: complete conversion of thin films taking place in seconds at 120 C. l

3. CONDENSATION BY Use or NON-VOLATILE, NON- Rssmous CATALYSTS The preliminary condensation of furfuryl alcohol can be effectively accomplished by the use of very active non-volatile catalysts such as sulphuric acid, phosphoric acid, ferric chloride, zinc chloride and similar dehydrating agents, but these materials continue to act after the initial condensation is completed with resulting instability of solutions and poor aging properties of films made from such products. It has been found that removal or inactivation of the catalyst after the preliminary partial condensation eliminates these undesirable features and allows the production of stable solutions which do not gel on storing and which give films which do not quickly become brittle. Because of their easy inactivation and removal, themineral acid catalysts are preferred, especially sulphuric acid. Condensation in the presence of solvents is preferred. An example of a process using sulphuric acid and removing it after the initial condensation is given below:

Example #3 Parts by weight Furfuryl alcohol 20,00 Acetone (solvent) 2000 sulphuric acid (sp. gr. 1.84) 30 C210 (for acid removal) 200 The concentrated sulphuric acid is first dissolved in the acetone and this acetone solution is then mixed with the furfuryl alcohol. The solution is held at room temperature, by cooling if necessary, for eight hours. After this treatment, samples will dry to tacky solid films in a few seconds at room temperature. The solution is then treated with an excess of dry calcium oxide or calcium hydroxide and stirred for a few minutes. The lime does not dissolve in the solution but reacts with the sulphuric acid, forming inactive, insoluble calcium sulphate. The solution is filtered and for best results, is again treated with lime and refiltered. Other neutralizing bases such as ammonium hydroxide, organic amines, alkali hydroxides, etc., may be used but the use of lime is preferred. The proportion of catalyst used canbe varied over a wide range as can the proportion of solvent. Increasing the proportion of catalyst causes quicker reaction and more spontaneous heating. Increasing the proportion of solvent has the opposite effect. The fitered solutions are stable and suitable for use in the preparation of the new wire enamels.

4. Connnuszrrron WITH NON-VOLATILE, REsrNoUs CATALYSTS Of the few materials which have been found to be compatible with furfuryl alcohol condensates and which produce improvements in film properties, the alkyd resins, particularly the fatty acid modified alkyd resins, are outstanding. Their use in conjunction with the initial condensates prepared by any of the foregoing methods will be shown later. that these materials themselves exert a catalytic efifect on the condensation of the furfuryl alcohol at elevated temperatures and therefore can be made to serve the double purpose of catalyzing the initial condensation and at the same time improving the flexibility, heat-resistance, durability and toughness of the films. As an example of the practice of this process the following is given:

Example #4 l l Parts by weight Furfuryl alcohol 671 Modified alkyd resin 6'71 The modified alkyd resin is dissolved in the furfuryl alcohol with the aid of gentle heating. The solution formed is then heated in a kettle fitted with a collecting condenser. At about 155 deg. C. an exothermic reaction sets in and continues for a while without the application of external heat. A light liquid consisting essentially of water and furfuryl alcohol distils during the reaction. The temperature is maintained at 155-165 C. untildistillation is completed. This requires about 2 hours. The last traces of water can be removed by adding some toluene to the contents of the kettle and distilling this out by further heating. The resulting material is a viscous, semi-solid mass having pronounced drying properties and being easily soluble in acetone, benzol and other solvents.

Such solutions, after filtering represent typical.

examples of the alkyd-modified furfuryl resin enamels of this invention. a

The initial condensation products formed in Examples 1, 2 and 3 can be dissolved in any suitable solvent such as acetone, ethyl acetate, benzol, toluol, etc., and mixed with solutions of modified alkyd resins to form the most desirable modifications for use as wire enamel. The product of Example 4 is already modified by the alkyd resin during its manufacture and needs no further additions. The products of Example 1 are preferred for use where further modification by alkyd resins i'sto be made after the initial condensation 'of the furfuryl alcohol. A typical wire enamel formulation is shown here.

Example #5 Parts by weight Furfuryl condensates (of Example 1) 10o 1-4P.B.W Acetone Modified alkyd resin 100 Acetone o -1 P. B. W.

It has also been found The two solutions shown are simplymixed together. The concentration of each solution and the ratio of the two solutions used can bevaried over wide limits.

The alkyd resins used are preferably the oxidizing type in which drying oil fatty acids are used to modify the glyceryl-phthalate.

Specific examples are:

Other resins of the same general type in which ethylene glycol, diethylene glycol, and other polyhydric alcohols are used to partially or entirely replace glycerol and in which maleic anhydride, sebacic acid, pimellic acid, succinic acid, Petrex- 3 isopropyl' 6, methyl 3,6, endoethylene A tetrahydro phthalic anhydride, or

other dibasic acids are used in place of phthalic anhydride are also suitable. The fatty acids used for modifying these materials may be obtained from many oils such as linseed, soy bean, perilla, Chinawood, etc.

The product of Example 4, thatis, a coating solution formed by the reaction or condensation have added to them prior to baking, one of the volatile catalysts which is inactive in the solution at normal temperatures but which acts as a catalyst at baking temperatures and is driven off as a vapor when the reaction is completed so as to prevent further action to cause deterioration upon aging.

The drawing discloses in Figures 1 and 2 an insulated conductor construction in which the conductor has applied thereto an insulation coating comprising a drying-oil modified alkyd resin combined with a condensate of furfuryl alcohol.

Wires enameled with furfuryl resins according to the present process have several advantages over the materials now used. They are equivalent to enameled wires of common manufacture in electrical properties and are much superior in regard to solvent resistance. The enamel will stand almost indefinitely at ordinary temperatures without deteriorating. The wire enameling oven at high speed the enamel is sumciently cured for spooling and handling. It has been found, however, that the product is greatly improved in aging properties and adhesion by heating the spooled wire for a long period at a rela tively low temperature, say for 16 hours at 110 C. This after-curing has been used to some extent for ordinary enamels to give a slight improvement; but with the present material the improvement is very much more pronounced. The extent of improvement by after-baking varies with the ratio of furfuryl resins to alkyd resins, being greater as the ratio of furfuryl resins increases.

It is thus seen that the preliminary treatment and the after treatment both contribute to the speeding up of the baking operation which heretofore has required the most time, equipment and cost. And the present materials, which have produced such outstanding enamels, could not be Example #8 Parts by weight Glycerol 92 Phthalic anhydride 194 Linseed fatty acids 110 Example #7 Parts by weight Glycerol 92 Phthalic anhydride 185 Linseed fatty acids 70 Chinawood fatty acids '70 Any of the partial condensation products may used at all in practice except for the preliminary partial condensation operation.

With prior processes requiring high baking temperatures the enamel is spoiled if the wire travel is halted even for a short time. With the present process permitting low baking temperatures the enamel is not injured even if the wire travel is stopped for a considerable time. Scrap loss from this cause is practically eliminated. Another beneficial effect is that the wire may be stopped for inspection whenever desired.

To reduce the expense it is possible in any of the examples to use a less expensive furan derivative with the furf'uryl alcohol.

The alkyd resins used may also be of the phenol-aldehyde modified type or may be added together with heat-convertible phenol aldehyde resins. Such modifications produce somewhat harder films which are less liable to mechanical injury when the hot, freshly baked wire is passed over sheaves.

It is to be understood that the invention may be variously modified within the limits of the prior art and the scope'of the subjoined claims.

I claim:

1. The method of producing an enamel for electrical conductors which comprises partially condensing furfuryl alcohol and adding to the partially condensed product a drying-oil modified alkyd resin and a solvent.

2. The method of claim 1 further characterized by this: that the resin is added to the alcohol at a preliminary stage in the process so as to assist in the condensationoi' the alcohol.

3. The'method 01' claim 1 further characterized by this: thatin the condensation step a compound containing the aldehyde of furane, may be substituted for a part of the alcohol.

4. A baked coating on wires comprising the combination of a drying-oil modified alkyd resin, with a resin produced by the partial condensation of furfuryl alcohol.

5. A flexible, tough insulating enamel for electrical conductors comprising a drying-oil modifled alkyd resin combined with a furfuryl alcoing process itself can be carried out along the hol condensate, said enamel being hard and having high resistance to abrasion and solvents.

6. A flexible, tough insulating enamel for electrical conductors comprising a drying-oil modified alkyd resin combined with a condensate of furfuryl alcohol and the aldehyde of furane, said enamel being hard and having a high resistance to abrasion and solvents.

HENRY J. KAUTH. 

